Generally steering torque variations experienced as disturbances can be mitigated by appropriate geometrical design of the steering mechanism and front suspension of a vehicle. This has proven to be hard to achieve in real life vehicles because of cost and packaging issues resulting in a less than ideal geometry.
The experienced amount of disturbances can also be diminished by using a high level of power support or other techniques like various types of filtering, friction and damping in the steering system that isolate the driver from variations of the required steering torque. This will unfortunately also isolate the driver from desired feedback signals in the steering system e.g. variations in self aligning torque and will have a detrimental effect on steering feedback and steering feel.
This problem is most evident in small front wheel driven cars with powerful engines and wide low-profile tires.
The prior art document EP 1 442 958 A2 shows a steering system comprising an open loop steering torque controller and an open loop steering angle controller. The open loop steering torque controller provides an output overlapping with the steering torque provided by a driver using the steering wheel. The open loop steering angle controller provides an output overlapping with the steering angle provided by a driver using the steering wheel.